Papers by Keyword: Vacuum

Abstract: A hydrostatic bearing using ionic liquid (IL) has been developed to float semiconductor wafers in a high vacuum chamber. In semiconductor manufacturing, it is important to suppress overheating of wafers and maintain a constant temperature distribution. This method aims to achieve uniform temperature distribution by supplying IL from the backside of the wafer to float it, thereby without mechanical contact. However, since there are no examples of wafers levitated by hydrostatic bearings using IL in a high-vacuum environment, the effect of circulating IL to the vacuum conditions such as vacuum pressure and outgassing were investigated in this study. Experimental results showed that the developed prototype machine was capable of maintaining a stable ultrahigh-vacuum of 10^-5 Pa and supplying sufficient pressure to levitate wafers even when 100 ml of IL was circulated.

Abstract: Thin films of tungsten oxide were deposited on glass substrates by the radio frequency (RF) reactive sputtering from a high purity tungsten metal target (99.9%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 20% of O₂ and 80% of Ar. The used RF power is 200 W while fixing the deposition time at 120 min. Finally, the prepared films were annealed at different temperatures (350 °C, 400 °C, 450 °C, 500°C and 550 °C) for 1 hour under air and under vacuum. X-ray diffractograms showed that the deposited thin films crystallized in Hexagonal/Monoclinic WO₃ phase. It was found that the crystallite size varies with the annealing temperature and the lattice parameters is a= 7.3064Å, b = 7.5292Å, c = 7.6875Å and a=b= 7.3242Å, c= 7.6624 Å, for h-WO₃ and m-WO₃ structures, respectively. Scanning Electron Microscopy (SEM), Raman spectra confirmed the formation of WO₃ thin films. In addition, optical transmittance data revealed that the optical bandgap of the films decreases with increasing the annealing temperature. Electrical measurements revealed that annealing in air results in more resistive samples, which should be taken into account in future investigations, especially as buffer layers for efficient photovoltaic solar cells. Keywords: Vacuum, Tungsten oxide, Raman spectroscopy, RF Sputtering method, RF Power, Annealing temperature.

Abstract: This article presents the results of studies considering the possibility of obtaining products based on phenol-formaldehyde oligomers of reduced toxicity, material consumption and corrosive activity. This is achieved by removing free phenol and formaldehyde monomers from the foaming composition and by more complete implementation of hydrodynamic processes during foaming of the composition. The article includes the results of studies on finding the ratio of the initial components and its effect on the corrosive activity of finished products. It is also considered the determination of the dependences of the toxicity and material consumption of phenolic foams on the pressure gradient of the foaming composition and the environment. For the research, the FRV-1A resole prepolymer and the VAG-3 foaming-hardening agent were used as raw materials. The content of phenol and formaldehyde monomers was determined by gas chromatography. In this work, the diagram of installation is developed and presented. It consists of a high-pressure machine, a mold, a vacuum pump, a vacuum gauge, air supply and air removal pipes. The results indicate that ensuring the formation of a cellular structure of phenolic foam in the low-pressure zone makes it possible to obtain heat-insulating products based on phenol-formaldehyde oligomers of reduced toxicity, material consumption and corrosive activity.

Abstract: In this work the composite made from epoxy resin as a matrix and natural fiber of Cordyline australis was used as reinforcement. The fiber was prepared from the process of water retting in fresh water for 1 weeks followed by drying. The final process was soaked in sea water to understand the effect of soaked in sea water to the adhesion of the fiber and matrix. The fiber was immersed in 5 hour and also 7 hours in sea water to be compared with the fiber that is was not immersed in sea water. The curing process also consist of 2 variation processes namely hand layup and vacuum pressure. The tensile test is conducted to investigate the final product of composite. It is found that the vacuum process resulting better tensile strength (34.610 MPa) in the sample of epoxy without fiber reinforcement (19.818 MPa for hand layup). In general for composite that are made with fiber without immersion in sea water, the tensile strength for the hand layup increase with addition of fiber fraction. In the other hand the tensile strength is decrease with addition of fiber fraction for vacuum process. For the fiber reinforcement, the hand layup resulting in better reinforcement comparing the vacuum process. .

Abstract: In this study, a thermal battery is designed with vacuum insulation to improve its thermal insulation. Thermal insulation is one of the many factors that determine the stability and operation of the battery. The battery’s operating time as well as the improvement in its thermal insulation performance were analyzed. The location of the vacuum insulation was set as a variable in the analysis models. The thermal battery was subjected to unsteady heat transfer analysis until the electrolyte temperature reached 450°C. Vacuum insulation was applied to the part of the base thermal battery to fabricate three model batteries. Compared with the base model B, the operating time increased by 48% for the model BS, 76% for the model BSB, and 179% for the model BSBT. Due to the large area of the side, a large amount of heat was transferred; the quantity of heat transfer was in the order B>BS>BSB>BSBT. In the model BSBT, the heat loss per unit area was reduced by 93% at the side, top, bottom compared with the base model. The results of this study will serve as basic data for the design of thermal batteries with vacuum insulation and for improvement in insulation performance.

Abstract: A procedure has been developed for calculating the geometric, kinematic and energy-power parameters of helical rolling, which allows a comparative analysis of the processes carried out in stands of various designs. Based on the results of this analysis, a helical rolling mill was designed and manufactured which allows to roll materials with high deformation resistance at high temperatures. The results of the study of the mechanical characteristics of molybdenum bars and wires made by new technology are presented.

Abstract: The high energy consumption of buildings in the various sectors of society, the exploitation of natural resources and the use of fossil fuels make it necessary to research constructive alternatives that can reduce the impact on the planet. The use of thermal insulation in buildings is important for the reduction of energy consumption, however, most of the materials developed are manufactured generating high rates of pollution. This study starts with the use of natural elements (corn cob / soybean straw / pine bark) and innovative elements (vacuum / slimstone plate), in order to improve energy efficiency of buildings. The methodological development of the work began in the selection of materials and development of facade cladding boards. The determination of the thermal conductivity was analyzed using a heating plate and PT100 temperature sensors, determination of the apparent and actual density, and analysis of the material composition using Scanning Electron Microscopy (SEM). After the development of the analyzes, the natural slabs and recycled slimstone showed significant results, with thermal conductivity lower than 0.07 W / m.k.

Abstract: Vacuum insulation panels (VIP) currently belong to a group of so-called super-insulating materials. These are special products with an extremely low equivalent value of the thermal conductivity coefficient. Despite this fact, the use of VIP in the construction industry is rather problematic. The main issue is the relatively complicated VIP integration into building structures, as well as the limited VIP durability. The issue of durability is also one of the main topics of VIP development and research in this field. The paper describes the possibilities of using CaO to increase the durability of vacuum insulation panels.

Abstract: This paper proposes a new vacuum sensor with CMOS Metal-N-Poly thermoelectric materials which works for both thermoelectric sensing and resistive heating. A new method of vacuum measurement with self-heating is proposed based on the dual phases of heating and sensing for the same element which is realized with CMOS thermoelectric sensor. Using the TSMC 0.35 μm CMOS-MEMS process, the proposed thermoelectric sensor is designed and fabricated with standard CMOS materials of the 4th metal and N-polysilicon to form 64 pairs of central-symmetrical thermocouples. There is an air convection-sensing area at the center of membrane and is filled with array of micro-through-holes to enhance the effect of heat convection. When the air molecules move through the array of hole, the heat exchange will take away the heat to cause a temperature drop of sensing area which gives a weak voltage between the cold and hot end of the thermocouples. The heating of thermopile itself is designed at the first phase and sensing the output voltage at the second phase subsequently. According to a careful investigation of the measurement with a wide range of 10m~10k torr, our proposed sensing scheme based on a thermoelectric type sensor is proved for practical vacuum detection and most of all it is proved as a new approach to use a commercial thermopile without heater, which is easier to include than a special custom design.

Abstract: An easy and fast vacuum detonation method was designed to prepare TiO₂/Na₂Ti₆O₁₃ powders. The mixed explosives, prepared by usage of Ti-Na-contained precursor, ammonium nitrate, hexogen and a certain mass of polystyrene foam ball (EPS) in beaker, were detonated in a vacuum detonation reactor to synthesize powders. The prepared light-grey powders were characterized by powder X-ray diffractometer and transmission electron microscopy to ascertain the phase composition and morphology. It was found that the powders were consisted of TiO₂ and Na₂Ti₆O₁₃, and the TiO₂ almost was rutile phase. The intensity of Na₂Ti₆O₁₃ peak was enlarged with increase of EPS mass. The TiO₂/Na₂Ti₆O₁₃ particles were irregular sphere or long rhombus, and some particles were 10 nm. In general, the dispersity of the powers was decreased with the mass of EPS increasing.